Conventionally, various kinds of copolymers having different physical properties have been synthesized by copolymerizing vinyl monomers alone or various vinyl monomer mixtures. Among them, since a polymer using a single vinyl monomer cannot satisfy various physical properties requirements, generally, a method of copolymerizing a mixture containing two or more kinds of vinyl monomers or a method of mixing different copolymers has been used. However, when merely copolymerizing various kinds of vinyl monomer mixtures, characteristics of each monomer unit have been tended to be averaged.
In addition, when merely mixing two or more kinds of copolymers, in many cases, the characteristics of the mixture thereof were inferior to those of each monomer unit without the copolymers being merged with each other.
In order to solve these problems, studies on copolymers using macromonomers have been conducted. The macromonomer is a high molecular weight monomer having a polymerizable functional group. The copolymer in which macromonomers are copolymerized is characterized in that individual properties can be expressed without impairing the properties of each of the macromonomer moiety and the monomer unit copolymerized with the macromonomer. Therefore, for example, various copolymers using this type of macromonomer have been also proposed in the field of adhesives.
For example, Patent Literature 1 discloses an adhesive composition containing a copolymer dispersed in an aqueous medium having a specific solid content by copolymerizing a macromonomer having a number average molecular weight of 2,000 g/mol to 50,000 g/mol and an ethylenic unsaturated monomer.
Further, Patent Literature 2 discloses a resin composition for an adhesive, which is obtained by copolymerizing an alkyl (meth)acrylate monomer and a macromonomer having a number average molecular weight of 1,000 to 200,000 and a glass transition temperature of 30° C. to 150° C.